The present invention relates to a fuel-injection control device for outboard motors. In particular, the present invention relates to fuel-injection control for low-speed operation of an engine.
Traditional internal combustion engines use a carburetor as a means for supplying a fuel-and-air mixture into the combustion chamber. A carburetor in the suction flow path of an engine takes advantage of the air sucked in by the engine and expels fuel in a mist form from a chamber inside the carburetor. The fuel mist mixes with the air and the resulting fuel-and-air mixture is sent into the engine.
To compensate for specific engine characteristics the operating demands of the automobile or marine environment, and the characteristics of the load driven by the engine (e.g., an automobile or a boat), the carburetor uses a combination of different jet types to provide an optimal setting. However, a carburetor cannot adapt continuously to changes in driving conditions and the surrounding environment. In particular, achieving a proper setting for the air-to-fuel ratio when the engine is started or during low-speed operation is difficult.
In recent years, engines with fuel-injection devices have been widely used as an alternative to carburetors. A fuel-injection device uses as its control parameters such factors as the temperature of the engine, the temperature of the water used to cool the engine, the air suction temperature, the engine boost pressure, the engine speed, the intake air temperature, the throttle setting, and so forth. It is clear to one skilled in the art that the above list of parameters is neither exclusive nor exhaustive, and a number of other parameters may be used also or in combination with the above list as control parameters for the engine. One or more of these control parameters defines the engine state. These control parameters are analyzed using a computer to determine a correction value. A fuel injector injects an amount of fuel appropriate at that particular instant directly into the air suction path of the engine. Thus, both combustion efficiency and engine output optimized. Also, fuel consumption is minimized, since only the minimum necessary amount of fuel is injected into the engine.
In outboard motors used in small marine vessels, the engine can be pivoted (trimmed) around a shaft on an attachment bracket. This provides increased efficiency from the propeller to correspond with the orientation and speed of the marine vessel. For outboard motors using a two-cycle engine, applying trim to the outboard motor results in a fuel residue remaining on the walls of a crank chamber within the engine and the inner walls of a surge tank. When fuel is left as residue at these locations, it is possible for there to be temporarily insufficient fuel introduced into the combustion chamber of the engine until the residual fuel becomes constant relative to the incline of the outboard device. This can result in a lean air-to-fuel ratio, which is undesirable. Also, depending on the magnitude of the change in the trim angle, there can be variations in the value at which the air-to-fuel ratio becomes lean as well as variations in the time required for the air-to-fuel ratio to return to normal and stabilize (see FIG. 9(a) and (b)).
Referring to FIG. 7, a sample correction map is shown for the magnitude of the change in the trim angle and the tailing time (i.e. the stabilization of the correction with time after a change in the trim angle).
Referring to FIG. 8, a relationship is shown between the correction continuation time and the change in the trim angle (magnitude and direction).
When the outboard device is trimmed down, the residual fuel left in the engine flows into the combustion chamber all at once. When the fuel flows into the combustion chamber all at once, there is an excessive fuel supply, resulting in a richer air-to-fuel ratio, which is not desirable. Also, depending on the magnitude of the change in the trim angle, there can be variations in the value at which the air-to-fuel ratio becomes rich as well as variations in the time required for the air-to-fuel ratio to return to normal and stabilize (see FIG. 9(c) and (d)).
Referring to FIG. 10(a), the residual fuel left in the engine is greater when the trim angle is larger.
Also, the residual fuel volume varies according to the operating state of the engine. Referring to FIG. 10(b), there is a higher residual fuel volume when the engine rotation speed is lower compared to when the engine rotation speed is higher.
Referring to FIG. 10(b), as in engine rotation speed, a lower engine temperature results in a higher residual fuel volume compared to a higher engine temperature. Referring to FIG. 10(d), there is higher residual fuel volume when the intake air temperature is lower than when the intake air temperature is higher.
As described above, the volume of residual fuel varies according to the operating state of the engine. In particular, residual fuel volume is high when the engine is operated at low speeds.
The use of corrections based on the trim angle of the outboard device to control the fuel supply volume has been disclosed in the past, such as in Japanese laid-open publication number 2-283833 and Japanese laid-open publication number 6-66177. In these references the fuel supply volume is corrected based solely on the trim angle of the outboard device, and no consideration is given to changes in the trim angle and the operating state of the engine. When the fuel supply volume is corrected based solely on considering the trim angle, the fuel can be too rich or too lean so that an appropriate air-to-fuel ratio cannot be obtained. This can result in white smoke in the exhaust gas and increased engine vibrations (when the air-to-fuel ratio is too rich), or in sudden engine stoppage (stall) (when the air-to-fuel ratio is too rich or too lean).